Keypads are commonly used to enter alphanumeric data. Conventional 12-key keypads formed of a four-row by three-column matrix of keys were developed when the telephone system changed from rotary dial to touchtone telephones. Each time the key of a touchtone telephone is depressed, a dual-tone multifrequency (DTMF) signal is generated. The two tones identify the key that was depressed. Originally, conventional 12-key keypads were used to enter numeric data—the integers from 0 to 9—plus the * sign and the # sign. As the telephone system evolved from a land line system to a cellular telephone system, and as telephone communication evolved from voice communication to data communication, the use of keypads has evolved and changed. Many modern keypads are used to enter text formed of the letters of the alphabet and symbols as well as numbers. Because the number of letters of many languages, such as the English language, is greater than the number of keys on 12-key keypads, in the past, multiple letters have been associated with selected keys of contemporary 12-key keypads. Multiple depressions of the selected keys in rapid succession result in the entry of a specific letter. For example, the number 2 key of a conventional 12-key keypad includes the letters A, B, C; the number 3 key includes the letters D, E, F, etc. Letters are entered into the memory of a related device, such as a cellular telephone, for example, by rapidly actuating, i.e., depressing and releasing, a particular key the number of times related to the letter. For example, in the case of the number 2 key, one actuation enters the letter A, two rapid actuations enter the letter B, and three rapid actuations enter the letter C. A predetermined interval after the last actuation results in the software that interprets the key presses spacing forward to the next letter position. The # sign key functions as a backspace key and is used to correct text entry errors. Obviously, entering text by the rapid actuation of selected keypad keys is both time consuming and error prone. As a result, various software and hardware proposals have been made to improve the data entry using keypads, in particular 12-key keypads. Some of these proposals have been implemented.
One software proposal is for the device employing a keypad to contain a dictionary of words stored in memory that are accessed as keys are actuated. More specifically, the key actuations are mapped to the words stored in memory using predictive software. One example of such a software proposal is the T9 text entry system. The T9 text entry system predictively compares single key actuations to dictionary words to enter text. For example, actuating in sequence the keys bearing the numbers 2 (A, B, C), 6 (M, N, O) and 3 (D, E, F) once would result in the entry of the word “AND” based on the prediction that “AND” is the most likely word that the user desires to enter. T9 type text entry systems usually have the ability to scroll to the next most commonly used word if a series of choices are available by pressing a non-letter key, such as the “0” key.
While T9 type text entry systems are an improvement over multiple actuation text entry systems, T9 type text entry systems have some disadvantages. For example, if a word is not in the dictionary stored in memory, it may be difficult, if not impossible, to enter a desired word. This disadvantage is of particular significance when a user desires to enter individuals' names, due to the wide variations in both family and given names.
In addition to software solutions to improve text entry using a 12-key keypad, hardware solutions have been proposed. One hardware proposal has been to include a rocker switch whose position determines the letter entered using a multiple letter key. Obviously, this approach requires additional hardware, which increases the complexity of keypads and, thus, the cost of producing keypads. Further, mechanical switches are subject to wear and breakage.
Another prior art hardware proposal is to overlay the keypad with a matrix of capacitive sensors, one associated with each key. When a user's digit, i.e., a user's finger or thumb, is moved along a predetermined path of travel over such a capacitive sensing system, a letter is entered. For example, moving a user's finger or thumb from the letter 5 to the letter 1 to the letter 2 to the letter 3 and back to the letter 5 may result in the entry of the letter “C.” One of the obvious disadvantages of this hardware solution is that the user's moving digit must remain within a predetermined distance of the capacitive sensor. Further, the movement must be continuous. These disadvantages, as well as the need to learn a specific path of travel for each letter or symbol to be entered, makes this proposal unacceptable in most environments.
In summary, prior software and hardware proposals for entering text using a keypad, in particular a conventional 12-key keypad, have not been entirely satisfactory. Consequently, a need exists for a new and improved text entry method using a keypad. Preferably, the solution will not require any change to the keypad hardware. Rather, the solution will be implementable in software, which is relatively easy and inexpensive to change.